Microwave Properties of Strontium Barium Niobate Thin Films Grown by Pulsed Laser Deposition

摘要

Strontium barium niobate (Sr_xBa_(1-x)Nb_2O_6 - SBN) with 0.25≤x≤0.75 is a ferroelectric material of interest for diverse optoelectronic applications. Dielectric properties of bulk SBN crystals were comprehensively studied over 30 years ago for a range of compositions and at frequencies up to 30 MHz, but there is little information on properties at higher frequencies. In particular, and up to the best of our knowledge, there are no published results about SBN thin film dielectric properties at high frequencies. For the study reported here, SBN thin films with x = 0.61 were grown on MgO and LaAlO_3 substrates by Pulsed Laser Deposition (PLD). Films with good crystallinity and oriented with c-axis normal to the substrate surface were obtained on both types of substrates, while films on MgO had much better texture due to better lattice matching. Interdigital electrode (IDE) capacitors and coupled microstrip phase shifters (CMPS) were fabricated with both types of samples in order to study dielectric response. Capacitance of the IDE capacitors was measured at 1 MHz as a function of temperature and bias voltage, revealing very low losses but poor capacitance tunability, particularly for samples on MgO. Response of the CMPS structures was measured at room temperature and at high frequencies, up to 21 GHz. Insertion losses were measured up to 28 GHz.